The present invention relates to the concept of determining an interference with a regulated voltage provided by a control loop, such as it may particularly be used to avoid loss of security-relevant data.
In electronic circuits, there are generally needed various stable voltages. In order to be able to provide these different voltage levels, voltage regulators are used, among other things. By exposing metal traces of an internal voltage supply network of an electronic circuit by preparation and subsequent contacting with the aid of a so-called probe needle and a so-called spike generator, interferences in the form of voltage peaks and/or spikes may be induced on an internal regulated voltage of the electronic circuit. Voltage peaks on the internal regulated voltage may, for example, result in malfunctions of a system linked to the electronic circuit, which may result in loosing security-relevant data. For example, in the field of cryptography, faulty results of an encryption algorithm due to outside influences, potentially in comparison with a correct result, may reveal security-relevant keys.
Contacting the internal voltage supply of an electronic circuit with a probe needle during a spike attack on a system requires impressing a DC voltage Vprobe corresponding to the internal regulated voltage VDDint. As an attacker generally does not exactly achieve the voltage level VDDint of the internal regulated voltage with the impressed DC voltage Vprobe, an intervention takes place into a control system of the internal voltage regulator, which then reacts with a permanent actual value>target value and/or actual value<target value.
Effects of an induced voltage peak on an internal regulated supply voltage may be detected by, for example, comparing two voltages derived from an external supply voltage of the electronic circuit. For this purpose, a voltage is, for example, influenced by capacitive launching of voltage peaks of the internal regulated supply voltage. With this procedure, however, an unambiguous distinction between legitimate load changes caused by the system and actually induced spikes is very hard to achieve and/or may only be realized with a large safe distance. This results in a dependence of the sensitivity of a voltage peak detector on an internal chip capacitance, a floor plan and the application.